Glass BSDF gets totally grey/white in cycles
In cycles, for a glass material you need to set the roughness to 0 and the IOR to 1.450 on a glass BSDF. For the viewport shading, it is not possible to make the glass transparent unless you switch to eevee rendering engine and adjust the materials (You'll have to learn about screen space reflections).
Edit: For more transparency:
With only glass shader:
With transparent and glass shader: